A continuous casting mold has a pair of broad faces or side walls which are separated by a pair of narrow faces or end walls to form a box-shaped mold for casting a continuous steel slab. In the casting process, the molten metal is poured through the cavity defined by the inner surfaces of the mold walls. As the molten steel moves through the mold, it partially solidifies, forming an outer skin layer. In order to efficiently dissipate the heat from the molten steel, the walls of the mold are typically formed of copper or have a copper alloy surface layer and contain numerous passages through which water flows during the molding process for rapid heat exchange.
The surfaces of the mold which contact the molten steel, both broad faces and narrow faces are typically referred to as the "hot faces" of the mold. As stated, these faces are generally made of copper or copper alloys due to copper's excellent thermal conductivity characteristics. In continuous casting, however, these surfaces are exposed to the extremely-high temperature molten steel and flux for prolonged periods of time. Under these conditions, the hot faces of the mold experience relatively rapid degradation or wear such as cracking and erosion. Thus, it would be desirable to provide hot face surfaces which are more resistant to thermal wear than conventional continuous casting mold surfaces.
In addition, it is known that in order to adjust the width of the cast steel slab, continuous casting molds are designed to permit movement of the end walls along the length of the sidewalls. A fluid-tight joint must be maintained, however, between the edges of the end walls and the broad face surfaces which they contact. Typically, substantial clamping forces are exerted by the sidewalls on the edges of the end walls to achieve the required seal. To adjust the spacing of the end walls, the clamping force is released from one of the side walls which allows the position of the end walls to be adjusted.
It will be appreciated that as the end walls are adjusted to create various widths of steel slabs, the edges of the end walls become worn as a result of their movement against the broad faces. This eventually erodes the edges of the end walls such that the thickness of the cast steel slab is reduced. That is, the distance between broad faces is reduced due to a gradual wearing away of the edges of the end walls.
A number of techniques have been proposed for resurfacing these worn edges in order to build up the eroded end wall surfaces. None, however, has proven to be entirely satisfactory from both a technical and economic standpoint. One such approach is known as fusion welding. The high thermoconductivity of the copper end walls and the tendency of copper to form a porous weld bead make fusion welding a less than satisfactory approach for reclaiming the edges of end walls in continuous casting molds. In addition, it has been found that fusion welding significantly degrades the wear resistance of the mold edge such that the repaired edge has a much shorter service life than the original material. Although fusion welding has been utilized with such materials as chrome-zirconium copper alloys, the resultant surfaces are susceptible to cracking and porosity and exhibit low hardness values.
Another approach which has been utilized in the past to repair worn down end wall edges is electroplating. Electroplating, however, is a very slow and expensive process when used to cover large surface areas such as those present on continuous casting mold end walls with a relatively thick deposit. It is also known that electroplated surfaces may lack the required uniformity and bond strength for mold end wall repair. Similarly, resistance welding and flash welding are not particularly well-suited for forming a layer of new material over a large surface area as required in the present invention.
In the past a welding technique referred to as "explosion welding" has been used to form metal laminates and the like. For example, two or more metallic plates to be bonded together may be placed on top of one another with an intervening space. A layer of explosive is applied to the upper metal sheet which can be detonated by means of a suitable primer. Through the shock wave of the detonation, the upper sheet is accelerated toward the lower sheet. Upon impingement, welding occurs. Examples of explosion cladding are shown in various patents such as U.S. Pat. No. 4,844,321 "Method for Explosive Cladding;" U.S. Pat. No. 3,238,071 "Process of Treating Explosively Clad Metals;" and U.S. Pat. No. 3,900,147 "Method of Cladding Metal Articles." To the applicant's knowledge, however, none of the prior art discloses or suggests the possibility of using explosive cladding techniques for the manufacture or repair of continuous casting mold surfaces.
Therefore, it is an object of the present invention to provide a continuous casting mold having hot face surfaces which are highly resistant to thermal and other degradation.
It is a further object to provide a method of manufacturing or repairing the hot face surfaces of continuous casting molds which provides superior wear-resistant characteristics.
Another object of the present invention is to provide a method for repairing worn down edges of continuous casting mold end walls in a manner which provides high wear resistance of the repaired surfaces equal to or better than that of the original end wall material.
It is a further object of the present invention to provide a method for applying a coating to continuous casting molds by which deformation of the mold section is avoided.
It is still a further object of the present invention to provide a method by which two matched end walls of continuous casting molds can be simultaneously repaired.